Pressure initiating primer system for projectiles

ABSTRACT

A primer system of this invention includes a housing substantially filled with liquid and containing a sealed primer in intimate association with the liquid such that when the projectile strikes a target with sufficient velocity, a pressure or shock pulse is created within the fluid which initiates the primer.

United States Patent Breed 1 June 10, 1975 PRESSURE INITIATING PRIMER SYSTEM 3.397.643 giejrcza et al l [0%221/5 3,489.08 l o rg e 4 [75] F F S TL S Z ed B t NJ 3,672,300 6/1972 Axelson et all 102/81 X nven or: an re oon on,

FOREIGN PATENTS OR APPLICATIONS [73] Asslgnee: Breed 598,718 10/1959 Italy .1 102/73 R [22] Filed: July 11, 1973 Primary ExaminerVerlin R. Pendegrass [21] Appl' 378l58 Attorney, Agent, or Firm-Learman & McCulloch [52] US. Cl. 102/73 R; l02/83 [5]] Int. Cl. F42c 1/10 [57] F T T [58] Field of Search 102/73 R, 81, 73 A, 76, A pflmef System Of f d a housing 102/82 33 substantially filled with l1qu1d and containing a sealed primer in intimate association with the liquid such that [56] References Cited when the projectile strikes a target with suffieierit ve- UNITED STATES PATENTS loclty, a pressure or shock pulse 15 created within the fluid which initiates the primer. 2,703,53! 3/1955 Graumann et al. 102/73 R 2,764,093 9/1956 McCuiston 102/8! X 10 Claims, 4 Drawing Figures PATENTEDJUH 10 I975 SHEET q MEDOE PATENTEDJUN 10 1975 m mEDOI PRESSURE INITIATING PRIMER SYSTEM FOR PROJECTILES BACKGROUND OF THE INVENTION All known munitions in existence today are initiated either through the use of a firing pin striking the sensitive surface of a primer or detonator or through the use of an electrical detonator. Electrical detonators are expensive and require an electrical power source. Most munitions, therefore, are initiated by means ofa firing pin contained in a fuze. In the case of projectiles the firing pin is usually driven into the detonator or primer when the nose of the projectile strikes the target. Such systems therefore do not function reliably on graze impacts, where the nose either does not strike the target or strikes it at too shallow an angle. Many systems have been devised to attempt to solve this problem, but in each case the fuze has become significantly more complex and the degree of graze sensitivity achieved has fallen short of what was desired.

The primer initiating system of the present invention overcomes these problems by using a pressure pulse in a liquid to initiate the primer. The pressure or shock pulse is created when the projectile grazes a target, for example, by the sudden change in velocity experienced by the fluid or by the shock in the fuze structure which is then transmitted to the fluid. It has been found that if the sensitive surface of the primer or detonator is in intimate association with the liquid, the pressure pulse is capable of initiating the primer or detonator. Thus, neither a firing pin nor an electrical system is required. The pressure pulse can come from forces arising in any direction providing they impinge on the detonators sensitive surface with sufficient energy.

When firing gun ammunition such as 20-40 mm projectiles it is desirable to have the projectile explode approximately l millisecond after the fuze strikes a thin target such as an aircraft fuselage, whereas this delay is not desired if a thicker, more rigid target is struck. This has been difficult to accomplish in conventional projectiles since I millisecond pyrotechnic delay mixes are very difficult to achieve. It has been found that when a gas bubble is intentionally left in the fluid of the primer initiating system of this invention, this delay is achieved when the projectile strikes a thin target.

SUMMARY OF THE INVENTION Briefly this invention consists of a projectile having a substantially liquid filled nose or housing which contains a detonator or primer with its sensitive surface in intimate association with the liquid. When the projec tile strikes a target at a sufficient angle and velocity a. pressure pulse is created in the fluid which initiates the primer or detonator which in turn initiates the booster which explodes the round.

One of the primary objects of this invention is to provide a detonating system which is capable of initiating the explosion of a projectile when the projectile strikes a target at extremely small graze angles.

Another object of this invention is to provide a graze sensing feature for projectiles which is simple and inexpensive.

A further object of this invention is to provide a detonating system whereby a slight delay functioning after impact is achieved on thin targets.

Other objects and advantages of this invention will be made apparent as the description progresses.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view of a fuze according to one embodiment of the invention for use with munitions projectiles;

FIG. 2 is a cross sectional view of an alternative detonator for use in the fuze shown in FIG. 1 to provide increased sensitivity;

FIG. 3 is a cross sectional view of the projectile fuze incorporating an ogive deforming sleeve; and

FIG. 4 is a cross sectional view of an alternative detonator design containing a shock reflector plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A fuze constructed according to the embodiment of FIG. I is shown generally at l and comprises a housing 11 adapted for connection to a projectile and within which is a ball rotor 2. The ball rotor carries a thinwalled container 9 within which is an explosive mix constituting a sensitive detonator 3. The housing includes a thin wall ogive 5 and the usual booster assembly 6. As shown in FIG. 1, the detonator 3 is in the armed position. The ogive includes a chamber 8 containing a fluid 10 in intimate association with the detonator container 9.

When the housing 11 strikes a target, even at a shallow graze angle, significant acceleration components are established both perpendicular and parallel to the fuze axis. These acceleration components create a shock wave in the fuze housing which is transmitted to the fluid and focused onto the detonator contained 9 by a spherical surface 12 at the leading end of the fluid chamber. In addition, the acceleration acting on the fluid through the ogive also creates a shock wave which is focused onto the detonator. These pressure pulses exert a force on the detonator 3 sufficient to initiate the sensitive explosive.

A sufficient acceleration component perpendicular to the fuze axis also will cause a deformation of the ogive due to its thin wall, the mass of the ogive tip 13 and the mass of the fluid 10. This deformation also causes a shock wave in the fluid.

When the projectile strikes a thin target such as 0.050 inch aluminum, the nose of the ogive 5 partially collapses creating a pressure wave within the fluid. It has been found that if a gas bubble or void 14 has been provided a time delay of approximately 1 millisecond can occur before the detonator 3 is initiated by the pressure pulse. In the case of 20 mm. ammunition this provides a travel of approximately 3 feet before the warhead is initiated which is highly desirable when the target is an airplane.

It has been found that for some designs the sensitivity of the detonating system can be increased by providing a small, sharp indentation confronting the detonator. This more sensitive detonator is shown in FIG. 2 and comprises a hermetically sealed container 20 containing the explosive mix 21 and sealed with a cover 22 which has an indentation 23 in engagement with the explosive. The greatest sensitivity is achieved if a void 24, except for the indentation, is left above the explosive mix. Alternatively, a compressible sponge or felt material can be used in place of the void 24. The indentation must be in intimate contact with the explosive, however, if the maximum sensitivity is to be achieved.

FIG. 3 shows a fuze similar to FIG. 1 with the addition of a self-destruct system. Those parts of FIG. 3 similar to the parts of FIG. I are represented by the same reference characters. The operation of this system is described in co-pending US. Pat. application Ser. No. 395,962, filed Sept. 10, l973, by Breed, Thuen, and Breed. In FIG. 3 the fuze is shown in the unarmed position. In this case, the fluid initiating system provides superior graze sensitivity while the primary firing pin system is used for point initiation and selfdestruct. In the design of FIG. 3, a sleeve 7 has been placed with a snug fit onto the outside of ogive 5. On graze impacts this sleeve moves parallel and perpendicular to the ogive tending to deform it creating a shock wave in the fluid.

An alternate method of increasing the sensitivity of the detonator to being initiated by shock is indicated in FIG. 4 wherein a thin reflector plate 32 is placed between the sensitive portion of the detonator mix 33 and the output portion 34. The shock wave which is transmitted to the sensitive mix by the fluid is then reflected by reflector plate 32, thus increasing the pressure within the mix and the probability of initiation.

Care must be taken especially in using the more sensitive detonator designs to prevent detonator initiation on projectile launch. This is accomplished by assuring that the detonator in the unarmed condition is at a sufficient angle with respect to the spin axis of the projectile that the pressure pulse is significantly attenuated in trying to pass through the clearance between the ball rotor and the ogive.

In practicing the invention to achieve the maximum sensitivity the detonator must be one of the sensitive detonators which generally contains a composition called NOL-l 30 in the sensitive portion of the mix. The

M55 detonator and M98 primer have been found particularly successful. The thickness of the detonator container, and the plate 32, preferably is less than about 0.005 inch.

For the purposes herein, the term deformable housing means any enclosure the internal volume of which upon alteration results in a pressure pulse within the liquid. The term primer means any sensitive explosive component including a detonator which is capable of being initiated in response to a pressure pulse.

Thus the numerous aforementioned objects and advantages among others are most effectively attained by means of the embodiments described herein. It should be understood that this invention is in no sense limited thereby but its scope is to be determined by that of the appended claims.

I claim:

1. A pressure initiating primer construction for munitions comprising: a housing defining a sealed chamber, said chamber having a wall which is deformable in response to the striking of a target by said housing; a liquid substantially filling the chamber; and a pressure sensitive, sealed primer carried by said housing in intimate association with the liquid, whereby the striking of a target by said housing and the consequent deformation of said wall create a pressure pulse within the liquid which impinges on the primer with sufficient energy to initiate the primer.

2. The construction according to claim 1 including means for mounting said housing on a munitions projectile.

3. The construction according to claim 2 wherein the projectile is a 20-40 mm. projectile.

4. The invention according to claim 1 wherein a gas bubble is provided in the liquid.

5. The invention according to claim 1 wherein said primer is sealed within a container, said container having an indentation therein confronting the primer.

6. The invention according to claim 5 wherein a void is provided between the primer and said container.

7. The invention according to claim 1 wherein said primer comprises relatively more sensitive and relatively less sensitive explosives, and including a reflector plate between the more sensitive and less sensitive ex plosives.

8. The invention according to claim 1 including a metal member less than about 0.005 inch thick engaging said primer and interposed between the latter and said liquid.

9. A pressure initiating primer construction for munitions comprising a housing having a wall which is deformable in response to the striking of a target by said housing, said wall defining within said housing a sealed chamber having a spherical surface at one end thereof; a primer carried by said housing in communication with said chamber at the opposite end of the latter; and a liquid substantially filling said chamber, whereby the striking of a target by said housing and the consequent deformation of said wall produces within said liquid a pressure pulse which is focused by said spherical sur face toward said primer.

10. The construction according to claim 9 wherein a gas bubble is provided in the liquid. 

1. A pressure initiating primer construction for munitions comprising: a housing defining a sealed chamber, said chamber having a wall which is deformable in response to the striking of a target by said housing; a liquid substantially filling the chamber; and a pressure sensitive, sealed primer carried by said housing in intimate association with the liquid, whereby the striking of a target by said housing and the consequent deformation of said wall create a pressure pulse within the liquid which impinges on the primer with sufficient energy to initiate the primer.
 2. The construction according to claim 1 including means for mounting said housing on a munitions projectile.
 3. The construction according to claim 2 wherein the projectile is a 20-40 mm. projectile.
 4. The invention according to claim 1 wherein a gas bubble is provided in the liquid.
 5. The invention according to claim 1 wherein said primer is sealed within a container, said container having an indentation therein confronting the primer.
 6. The invention according to claim 5 wherein a void is provided between the primer and said container.
 7. The invention according to claim 1 wherein said primer comprises relatively more sensitive and relatively less sensitive explosives, and including a reflector plate between the more sensitive and less sensitive explosives.
 8. The invention according to claim 1 including a metal member less than about 0.005 inch thick engaging said primer and interposed between the latter and said liquid.
 9. A pressure initiating primer construction for munitions comprising a housing having a wall which is deformable in response to the striking of a target by said housing, said wall defining within said housing a sealeD chamber having a spherical surface at one end thereof; a primer carried by said housing in communication with said chamber at the opposite end of the latter; and a liquid substantially filling said chamber, whereby the striking of a target by said housing and the consequent deformation of said wall produces within said liquid a pressure pulse which is focused by said spherical surface toward said primer.
 10. The construction according to claim 9 wherein a gas bubble is provided in the liquid. 